1. Field of the Invention
The invention relates to the field of thermal turbomachines, in particular to a rotor end piece for rotors, and to a method of fitting a rotor end piece.
2. Brief Description of the Related Art
Thermal turbomachines including axial-flow turbines and axial-flow compressors have a rotor fitted with moving blades and a stator in which guide blades are suspended in order to guide the flow.
The task of the stationary guide blades is to direct the flow of the gaseous medium to be compressed or expanded onto the rotating moving blades of the respective compressor stage or the respective turbine stage in such a way that the energy conversion is effected with the best possible efficiency.
Both moving blades and guide blades essentially have a profiled airfoil and a blade root. In order to be able to fasten the moving blades on the rotor or the guide blades in the stator, slots are recessed in the stator and on the rotor shaft. The roots of the blades are pushed into these slots and locked there.
It is known that compressor blade rows of gas turbine rotors are arranged in circumferential slots, which often have a T-shaped cross section. As a rule, blades and intermediate pieces alternate with one another here. During the fitting of such blade rows, a special solution has to be found for the last blades to be fitted, since the remaining fitting opening for a complete intermediate piece is then too small. This residual opening is therefore filled with a “rotor end piece”.
DE 812 337 discloses such a rotor end piece. The known rotor end piece consists of an intermediate piece divided in half, that is to say of two end piece halves split in the circumferential direction with respect to the rotor, and of a wedge, by means of which the end piece halves are caulked in the rotor in the circumferential direction.
In the known prior art according to DE 812 337, the two end piece halves each have a straight side face. These side faces are opposite one another in the installed state, the wedge then being located between them. Once the two end piece halves and the wedge have been installed, the tabs formed on the top side of the wedge are finally bent into corresponding undercuts in the side faces of the end piece halves, and the wedge and thus the entire end piece are secured against flying out.
A disadvantage with this prior art is that, at high rotor speeds, strength problems may occur on account of the tilting moment of the two end piece halves, which is caused by the centrifugal force during operation.
A further disadvantage of these technical solutions consists in the fact that end pieces exert axial forces on the rotor, on the one hand due to the centrifugal force during operation and on the other hand due to the caulking of the wedge. In the search for the causes of the frequently occurring rotor vibrations, it has been found that these axial forces can bend the rotor and thereby adversely generate disturbing vibrations.
EP 1 215 367 A2 and DE 103 10 432 A1 describe solution proposals in which the forces are directed into the adjacent blades, i.e., in the circumferential direction. The solutions presented here are complicated and costly to fit and produce. In addition, rotor vibrations may also be caused by the introduction of the forces in the circumferential direction.